1. Field of the Invention
The present invention relates to a maintenance method of a wind turbine generator, and especially relates to a method for carrying out a maintenance work which involves detaching the nacelle from the tower.
2. Description of the Related Art
Some maintenance works of a wind turbine generator involves detaching the nacelle from the tower. Such maintenance works include replacement of the yaw rotation bearing or a bearing seal, adjustment of a shim attached to the tower-top flange, painting of the outer ring of the yaw rotation bearing, and repair of the lower part of the nacelle cover.
In a case where a maintenance work is carried out after detaching the nacelle from the tower, the nacelle is detached from the tower and is landed on the ground by using a large size crane, and then the intended maintenance work is carried out. However, in the procedure of such maintenance work, there are two problems. Firstly, in order to land the nacelle by using the large size crane, a lot of machinery and much manpower are required, and legal preparation (for example, a road-use permission and so on) is required. This means that the maintenance work requires great costs and a long period for the maintenance. Secondary, a large site is required to place the nacelle and the wind turbine rotor. The area of the site required for the maintenance may reach several dozen meters square. This restricts flexibility of the maintenance. If the maintenance which involves detaching of the nacelle from the tower can be carried out without using a large crane, a large merit would be obtained in reduction of the cost due to simplification of the maintenance and in improvement of the flexibility of the maintenance work.
As a related prior technique, Japanese Patent Application Publication No. 2006-22675A discloses a technique for constructing a tower of a wind turbine generator without using a large size crane. In the technique described in this publication, a mast is inserted into the tower and the nacelle is mounted on the tower and a pushing-up member capable of moving upward and downward relatively to the mast is additionally attached to the mast. In the construction of the tower, the mast is lifted up by applying a reaction force to an already constructed part of the tower via the pushing-up member, and subsequently the pushing-up member is lifted up. After that, the expansion part of the tower is constructed between the already-constructed part of the tower and the pushing-up member. The tower is completed in the same manner, by repeating: the lifting of the mast and the construction of the expansion part of the tower. After the completion of the tower, the mast is removed, and the nacelle is fixed to the tower.
In addition, Japanese Patent Application Publication No. 2002-248560A discloses a technique for replacing a rotation bearing after lifting up a heavy swivel. In this technique, the swivel is lifted up from a pedestal by a lifting jack provided on a placement table placed on a floor surface, and after that, the rotation bearing is replaced. After the replacement of the rotation bearing, the swivel is returned to the pedestal.